1. Field of the Invention
This invention relates generally to a vehicle battery which contains an article of manufacture which diminishes the effects of vibration on the useful life of said battery and, more particularly, to a plaque which is inserted during manufacture between the end cell element and the container end wall on each end of the battery to protect the end cell element from the flexing of the container end wall.
2. Description of the Prior Art
The fact that vibration reduces the useful life of a vehicle battery is well known. With the ever-increasing need and desire for vehicles which can be used for a variety of transportation needs from heavy-duty moving and hauling, both off-road and over the highway, to recreational travel, including marine applications, there is a need for the vehicle battery to withstand a much greater degree of vibration in order to ensure a satisfactory useful life.
Traditionally, protection from the effects of vibration in batteries has been accomplished by anchoring the elements of the battery to the bottom of the container by means of a layer of epoxy or "hot melt." Nevertheless, a particularly damaging mode of vibration in thin-walled polypropylene batteries exists despite the use of the epoxy anchoring method. It is the flexing in and out of the battery container end walls due to the varying hydraulic pressure of the electrolyte contained within the outermost cells. The oscillating hydraulic pressure is induced by the positive and negative "G" forces of the dynamic motion environment in which the battery operates. This phenomenon is commonly referred to as "oil canning." When the end walls of the battery container flex, the plates next to the end walls also flex and the lugs can eventually become detached from the straps, resulting in element imbalance which rapidly causes additional damage to the battery. The lugs and straps are the structural and electrical interconnections of the battery elements. Additionally, anchoring the battery elements with epoxy or "hot melt" can be a messy and labor intensive process leading to increased manufacturing costs.
The assignee of this application previously manufactured a model EV2300 battery which contained "reinforcement sheets" inserted between the end cell elements and the container walls to achieve 7 to 8% compression of all battery elements within the container, thereby increasing the electrical cycle life. The reinforcement sheets also improved handling characteristics (e.g. carrying, packing, stacking, etc.) of the battery. They were made out of polyphenylene sulfide and had a flexural modulus of greater than 1,000,000 psi. The flexural modulus is a measure of the stiffness of a material derived from ASTM test #D790-86. Greater stiffness will result in a higher flexural modulus. The EV2300 battery was never tested for compliance with the SAE "Off-Road" Vibration Specifications (J930), testing which subjects the battery to conditions of excessive vibration. Nevertheless, it is believed that the EV2300 reinforcement sheets would have been successful in reducing the effects of vibration to some degree.
The EV2300 reinforcement sheets were in the shape of the battery elements themselves, covering only that area of battery container walls below the straps extending across the elements. The substantial area of the container wall above the top edge of the elements was not reinforced. Also, installation of these sheets required expensive off-production line manufacturing, because the last element inserted into the battery had to be tapped in with a mallet in order to attain the compression necessary to achieve the desired effects. The EV2300 battery was, therefore, not extensively produced or marketed.
It is therefore desirable to provide a vehicle battery which alleviates the structural wear occurring in the dynamic operating environment and which is easier to manufacture than prior batteries.